In the context of satellite telecommunications, the needs of the operators are moving towards smaller and smaller terminals, of A4 or A5 size, or terminals of PDA (Personal Digital Assistant) type or telephones, to reach roaming users.
Numerous applications also relate to the trend among existing systems for internet or high bit rate applications.
To achieve these missions, the antenna architectures are increasingly complex, comprise a large number of feeds associated with numerous amplifiers to ensure the generation of around a hundred or several hundreds of increasingly narrow beams and provide continent-wide or worldwide coverage. The beams are formed either with a digital beam forming network BFN on board the satellite, or via a ground-based beam forming GBBF device.
For narrowband applications and for low frequency bands below 10 GHz, such as the L or S bands, it is difficult to multiply the number of antennas given their large size, generally 9 to 15 m, or even 20 m, in diameter for the deployable reflectors. In this case, it is known to use one or two active antennas placed in front of the beam forming reflectors being produced either on board in an analogue or digital way or by a device on the ground.
For wideband applications and for high frequency bands greater than 10 GHz, the digitization techniques are limited in the on-board band processing capacity, in the complexity and technological feasibility of the beam forming network BFN and above all in the excess energy consumption at the payload level. Generally, the payload is configured passively with a structure whereby a feed corresponds to a particular beam. For reasons of inter-beam isolation constraints and gain performance reasons, this means multiplying the number of antennas on the satellite according to the frequency reuse scenario from one spot to another. This scenario is called three- or four-colour code and generally necessitates an antenna for each frequency subband, or colour, used.
It is known to use beam synthesis with a network of individual feeds placed at the focus of a parabolic reflector and by reusing feeds from one spot to another as described notably in the patents EP 0340429 and EP0333166. These architectures allow for the use of compact antennas with a low F/D ratio, F being the focal distance and D the diameter of the reflector, and make it possible to tighten the beams, but give strong aberrations in the case of unfocused operation.
It is also known to produce radiant structures comprising a set of individual feeds coupled together by electromagnetic radiations and making it possible to radiate waves in phase, as described notably in the patents EP0899814 and EP0617480. These structures are excited by an individual feed powered by a radio frequency-type excitation signal originating from a channel of the satellite's payload.